1. Field of the Invention
This invention relates to a Stirling engine having a heating unit which is formed by using pipes.
2. Discussion of the Related Art
A Stirling engine of this type has been disclosed by Japanese Utility Model Unexamined Publication No. Sho 63-45050. The conventional Stirling engine comprises: a cylinder having an expansion space; a housing accommodating a heat accumulating unit, and a heating unit through which the expansion space is communicated with the heat accumulating unit. The heating unit is formed by using a number of heater tubes circular in section. The operating fluid in the heater tubes is heated by a combustion device (not shown).
As described above, the heating unit is formed by using a plurality of heater tubes. Hence, it takes a number of assembling steps to connect those heater tubes to the cylinder and the housing. The number of assembling steps may be decreased by employing one heater tube instead of the plurality of heater tubes in such a manner that the product of the sectional area of the flow path in the one heater tube and the length of the heating unit (hereinafter referred to as "a dead volume") is equal to the sum of the dead volumes of the plurality of heater tubes. However, in this case, the surface area of the one heater tube is much smaller than the sum of the surface areas of the plurality of heater tubes. That is, the heating unit formed by using one heater tube, is insufficient in heat transfer area, so that the amount of heat transferred to the inside of the heater tube from the combustion device is small.